If you mean email addresses and passwords are appearing automatically at the log in page, go to Security in your browser Preferences, then Security, and delete the details from your 'Saved Passwords'...
Double click in the text box and a list of all the stored entries should come up, use the up/down arrow keys to select the one you want to delete and press delete.
if that doesn't clear the ones you don't want then clearing your browsers form history will clear all of them and then just put the ones back in you want again.
Hi, thank you for all your help, but where can I find the browser preferences bit to click on?? As you most likely notice I am a bit of a duffer at this . Many thanks